VW Touran Glow Plug Failure: Control Unit Alert

As someone with moderate experience maintaining diesel engines, I had a very similar issue with my 2020 VW Tiguan diesel last winter. The symptoms matched yours exactly, persistent preheating lamp, engine misfire symptoms, and the same smoke issue during acceleration. Initially thought it was the glow plugs themselves, but after taking it to the workshop, they diagnosed a faulty cable connection to the glow plug control unit. The connector had corroded, causing intermittent contact issues. The repair involved cleaning the connection points and replacing a damaged wiring section. Total cost was 95€ and completely resolved the cold start problems. For proper diagnosis, could you share: Does the issue occur more frequently during cold weather? Have you noticed any changes in fuel consumption? Does the engine management light flash or stay constant? What were the exact error codes from the diagnostic test? As car maintenance issues can vary between different engine variants, knowing these details would help determine if your problem matches what I experienced. Regular glow plug system checks are crucial for diesel engine performance, especially during colder months.

Latest service was performed at 126000km. You raise some good points about the diagnostic approach. In my case, the error codes from the diagnostic test were P0380 and P0670, both pointing to the glow plug control unit circuit. The engine management light stays constant rather than flashing. The vehicle stalling occurs more frequently during cold mornings, and fuel consumption has increased by about 2L/100km since these symptoms started. The diesel engine seems particularly sluggish during the first 5 minutes of operation. The corrosion issue you mentioned is interesting, I had my mechanic check the connections, but they appeared clean. This suggests my problem might indeed be the control unit itself rather than just wiring. Will have the workshop perform a complete glow plug system inspection to confirm.

Thanks for providing those details about the error codes and symptoms. After seeing the codes P0380 and P0670 on your Touran, I'm even more convinced your issue differs from what I experienced with my Tiguan. Those specific codes combined with increased fuel consumption and cold start issues strongly suggest a failing glow plug control unit rather than just connection problems. When my Tiguan had similar symptoms but different error codes, cleaning the connections was enough, but your case matches a more serious control unit failure pattern. During the complete glow plug system inspection, have them check: Individual glow plug resistance values, Control unit input voltage, Wiring harness continuity The repair cost for a new control unit typically runs around 350€ plus labor. While not cheap, it beats the alternative of continuing to run with poor cold starts and engine misfires that could cause long-term engine damage. If they do replace the control unit, make sure they clear all error codes and verify proper cold start operation. This should resolve both the persistent preheating lamp and the smoke during acceleration.

Appreciate all the detailed feedback. After having the complete inspection done, it turns out you were absolutely right about the control unit being the culprit. The technician found that while all glow plugs tested within spec and wiring was intact, the control unit itself was failing to properly regulate the heating element timing. The replacement cost came to 380€ including labor, slightly more than estimated but worth every cent. The car maintenance report shows the new unit is performing exactly as it should. Cold start problems have completely disappeared, and the diesel engine runs smoothly from startup. No more smoke during acceleration, and fuel consumption has returned to normal levels. Really glad I didnt waste time trying cheaper fixes first. The systematic diagnostic approach you suggested helped pinpoint the exact issue. The engine misfire symptoms are gone, and the preheating lamp now functions normally. Will definitely keep up with regular glow plug system checks going forward to prevent similar issues.